Appendix_A.fm Page 18 Friday, October 22, 2004 1:09 PM
Handbook
Phase Diagram of Carbon
Group 4A
Pressure (atm)
106
Physical Properties
• Group 4A elements are all
solids at room temperature.
C
Carbon | known since
ancient times
Carbon
12.011
Si
2
8
4
Silicon
28.086
32
Ge
2
8
18
4
Germanium
72.59
50
Sn
2
8
18
18
4
Silicon | discovered in
1824 by Jöns Jacob
Berzelius
Tin | known since
ancient times
Tin
118.69
82
Pb
Lead
207.2
2
8
18
32
18
4
Lead | known since
ancient times
102
Graphite(s)
101
Vapor
0
5000
4827
4000
>3562*
Density
12
bp
mp
3280
2850
3000
2000
2623
1751
1420
945
1000
0
2000 4000 6000
Temperature (C)
Graphite is more stable than diamond
at STP, but the activation energy is
too high for diamond to change to
graphite at these conditions.
Melting and Boiling Points
Germanium | discovered
in 1886 by Clemens
Winkler
Temperature (C)
14
• Diamond, graphite, and
buckminsterfullerene are
three allotropes of carbon.
103
C
Si
232
327
Ge Sn
Pb
9
7.26
6
3
0
*diamond
11.34
5.32
2.27* 2.34
C
Si
Ge
Sn
Pb
M. Claye/Photo Researchers
2
4
Liquid
104
100
Density (g/cm3)
6
• The metallic properties of
Group 4A elements increase
from carbon to lead.
Diamond(s)
105
*graphite
• Carbon is found in nature as an element,
in Earth’s atmosphere as carbon dioxide,
in Earth’s crust as carbonate minerals, and
in organic compounds produced in cells.
• Silicon can be produced by the reduction
of silicon dioxide (silica) with magnesium,
carbon, or aluminum. Example:
SiO2(s) 2Mg(s)
Si(s) 2MgO(s)
• Tin is prepared by reduction of the
mineral cassiterite, SnO2.
SnO2(s) 2C(s)
2CO(g) Sn(s)
• Lead is refined from the mineral galena,
PbS. Galena is heated in air to form a
mixture of PbO and PbSO4. Lead is
produced through further reaction of
these compounds with PbS.
R18 Elements Handbook
Mark A. Schneider/ Photo Researchers
Sources
Al2SiO5
andalusite
Fe2SiO4
AlSi2O5OH
olivine
pyrophyllite
About 90% of the minerals in Earth’s crust are
silica and silicates. In silicates, each silicon
atom is surrounded by three or four oxygen
atoms. These units can be linked together in
chains, sheets, rings, or crystals.
Harry Taylor/ Dorling Kindersley
Elements
Appendix_A.fm Page 19 Monday, June 21, 2004 6:59 AM
First Ionization Energy
Atomic Properties
• Group 4A elements have
an electron configuration
that ends in ns2np2.
1086
900
786
761
708
Electronegativity
Energy (kJ/mol)
1200
Electronegativity
715
600
300
• For Group 4A elements, the
most common oxidation
numbers are 4 and 2. For
carbon, 4 is also common.
0
• Silicon and germanium are
semiconductors.
Atomic
radius (pm)
C
Si
Ionic
radius (pm)
Ge
3.0
2.5
2.0
1.8
1.8
1.8
1.9
Si
Ge
Sn
Pb
1.0
0
Sn
Pb
C
77
Si
109
Ge
122
Sn
139
Pb
175
15
C4+
41
Si4+
53
Ge4+
71
Sn4+
84
Pb4+
C
4
When carbon and silicon form four covalent
bonds, there is often sp3hybridization. The result is
compounds and ions with tetrahedral structures.
methane molecule
silicate ion
Important Compounds and Reactions
• Group 4A elements are oxidized by halogens.
Example:
Ge(s) 2Cl2(g)
GeCl4(l)
• Group 4A elements combine with oxygen to
form oxides. Example:
Sn(s) O2(g)
SnO2(s)
• Complete combustion of hydrocarbons yields
carbon dioxide and water. Example:
CH4(g) 2O2(g)
CO2(g) 2H2O(l)
H 890 kJ/mol
• Plants use carbon dioxide to produce
carbohydrates and oxygen.
• Aqueous sodium silicate, Na2SiO3, is used as
an adhesive for paper, as a binder in cement,
and to stabilize shale during oil drilling.
SiO2(s) 2NaOH(aq)
Na2SiO3(aq) H2O(l)
• Acetylene is a fuel used for welding. It forms
when calcium carbide and water react.
CaC2(s) 2H2O(l)
C2H2(g) Ca(OH)2(aq)
• Tungsten carbide, WC, is used on the cutting
surfaces of drill bits and saw blades.
• Lead(IV) oxide, PbO2, is used as electrodes in
lead acid car batteries.
Gabe Palmer/CORBIS
• Tin(II) fluoride, SnF2, is used in toothpaste to
prevent tooth decay.
Silicon dioxide, SiO2, is the
sand on many beaches and
is used to make glass.
Group 4A
R19
Appendix_A.fm Page 20 Monday, June 21, 2004 6:59 AM
Elements
Handbook
Group 4A
C
Green Chemistry
The term green chemistry was coined in 1992. It describes the effort
to design chemical processes that don’t use or produce hazardous
substances. The goal is to protect the environment and conserve
resources. For example, if a catalyst is used to reduce the temperature
at which a reaction occurs, the process requires less energy.
Decaffeinating Coffee
Carbon dioxide is at the center of a green chemistry success story.
Organic solvents are used to dissolve substances that are insoluble
in water. Many of these solvents are toxic. It can be difficult to
remove all traces of the toxic solvent from reaction products and
safely recycle or dispose of the solvent. Supercritical carbon dioxide
can replace some organic solvents.
Extraction
A gas becomes a supercritical fluid at a temperature and pressure
called its critical point. For carbon dioxide, this occurs at 31.1ºC
and about 100 atmospheres. At its critical point, carbon dioxide
is in a hybrid state. It has a high density (like a liquid) but it
is easily compressed (like a gas). Many organic compounds
dissolve in supercritical carbon dioxide. The solvent is easily
separated from a reaction mixture because it evaporates at room
temperature and pressure. It is also used to separate substances
from mixtures. It can extract caffeine from coffee beans, dryclean clothes, or clean circuit boards. ■
Si
Caffeine dissolves
inside coffee beans
soaked in water.
Caffeine diffuses into
supercritical CO2.
Absorption
Water droplets leach
caffeine from CO2.
After the caffeine is extracted, the
coffee beans are dried and roasted.
The aqueous solution of caffeine is
sold to soft drink manufacturers.
Optical Glass
R20 Elements Handbook
Elizabeth Simpson/Getty Images
Glass is a material with the structure of a liquid,
but the hardness of a solid. In most solids, the
particles are arranged in an orderly lattice. In
solid glass, the molecules remain disordered,
as in a liquid. The main ingredient in most
glass is silica (SiO2), which is one of the few
substances that can cool without crystallizing.
The glass used in eyeglasses, microscopes,
and telescopes is called optical glass. It is
purer than window glass and transmits more
light. Optical glass can be drawn into long
fibers that are used like tiny periscopes to
view tissues deep within the human body.
In an optical fiber, light travels through a
thin glass center called the core. A second
glass layer reflects light back into the core.
An outer plastic layer protects the fiber
from damage.
When the fibers are bundled into cables,
they often replace electrical cables in
computer networks. They are also used to
transmit television signals and phone calls
over long distances. ■
Appendix_A.fm Page 21 Monday, June 21, 2004 6:59 AM
Si
Beyond Buckyballs
Buckminsterfullerene (C60)
is one member of a family of
fullerenes. These structures
are closed-cage spherical or
nearly spherical forms of
elemental carbon. The cages
are networks of 20 to 600
carbon atoms.
Silicon is a semiconductor. In its pure form,
it conducts an electric current better than
most nonmetals but not as well as metals.
But its ability to conduct can be changed
dramatically by doping, or adding traces
of other elements, to the silicon crystal.
Scientists have verified the
existence of nesting spheres
of fullerenes. C60 can be
nested inside C240, and this
pair can be nested inside C540.
These nesting structures are
sometimes called buckyonions because they resemble
the layers of an onion. ■
Combinations of n-type and p-type semiconductors are used
to build tiny electronic components. An integrated circuit
containing millions of components can fit on a semiconductor
wafer that is smaller than a fingernail! The resulting “chip”
can control a computer, portable CD player, calculator, or
cellular phone. ■
Alfred Pasieka/ Photo Researchers
With a cellular phone, you can call your
friends from almost any location. You can
play a video game, read e-mails, or get the
latest news. You may even be able to take
and send digital photos. How can such a
complex device be small enough to fit in
your pocket? Semiconductor technology
is responsible.
Doping with arsenic produces a donor, or
n-type, semiconductor. Each arsenic atom
has five valence electrons, compared with
four for silicon. So there are extra electrons
in the crystal. Doping with boron produces
an acceptor, or p-type, semiconductor.
Because boron has only three valence
electrons, there is a positive “hole” in the
crystal for every boron atom. The extra
electrons or holes are free to move and
conduct an electric current.
2003 Jeff J. Daly/ Fundamental Photographs
C
Semiconductors
Dr. Sumio Iijima discovered a
tubular fullerene, or carbon
nanotube, in Japan in 1991.
A cell phone’s integrated
circuit must process more
and more data as features
are added to the phone.
?
Did You Know...
One name for diamonds is “ice.”
A diamond can quickly draw heat from
your hand when you touch it. Such a
high thermal conductivity is unusual for
a substance containing covalent bonds.
Group 4A
R21
Appendix_A.fm Page 22 Friday, October 22, 2004 9:48 AM
Elements
Handbook
Greenhouse Gases
There are gases in Earth’s atmosphere that are
called greenhouse gases because they act like
the glass in a greenhouse. Sunlight easily passes
through these gases to Earth’s surface. Some of
the solar energy is reflected off the surface as
infrared radiation. This radiation is absorbed
by greenhouse gases and radiated back to
Earth. By trapping infrared radiation, the
greenhouse gases keep Earth’s surface about
33°C warmer than it would be otherwise.
Carbon dioxide (CO2) is the most abundant
greenhouse gas. It is released into the air as a
product of cellular respiration and removed
from the air during photosynthesis. Such
interactions normally keep the amount of
atmospheric CO2 in check. But the burning of
fossil fuels releases more than 20 billion metric
tons of CO2 every year. Also, as forests are
cleared for agriculture, the ability of plants to
remove CO2 from the atmosphere is reduced.
With an increase in greenhouse
gases, more infrared radiation is
trapped, causing global warming.
The glass in a
greenhouse
traps infrared
radiation.
Scientists agree that a rise of only a few degrees
in Earth’s temperature could cause problems.
They disagree on how severe the problems
could be. Could climates change so that farmlands become deserts? Could the melting of
ice caps cause sea levels to rise until coastal
cities are under water? ■
Average Temperature at Earth’s Surface
Temperature (ⴗC)
C
Nigel Cattlin/ Photo Researchers
Group 4A
14.6
14.4
14.2
14.0
13.8
0
1950
1975
Year
Si Composite Materials
StockByte/ PictureQuest
Most composites contain two distinctly
different materials. The materials can be
arranged in layers as when a sheet of plastic
is sealed between panes of glass. Or a composite
may consist of a matrix in which fibers of
a second material are embedded. Often, the
matrix is plastic. The fibers can be carbon.
When a hockey stick
has a composite shaft,
there can be a quicker
release of the shot.
R22 Elements Handbook
Polycrylonitrile (PAN) is used to make some
carbon fibers. PAN fibers oxidize when they
are heated in air. The chains of aromatic rings
that result are then heated in the absence of
air. The chains fuse into long thin ribbons of
almost pure carbon, which pack together in
stacked layers.
Composites reinforced with carbon fibers are
stronger than steel, yet light in weight. These
composites are used in sports equipment, such
as hockey sticks and golf clubs. It is less tiring
to swing a tennis racket made from a carbonfiber composite than one made from wood or
metal. Carbon-fiber baseball bats act more
like wood bats than do aluminum bats. ■
2000
Appendix_A.fm Page 23 Monday, June 21, 2004 6:59 AM
Recycling Plastics
C
PhotoDisc/Getty Images
At about 2 kg of waste per person per
day, the United States leads the world
in the production of solid waste.
Luckily, the United States is also a leader
in recycling. It is important to recycle
plastics because they are made from
crude oil, a non-renewable resource.
Also, some plastics release toxic gases,
such as hydrogen cyanide (HCN) and hydrogen chloride
(HCl), when they burn in an incinerator. Finally, plastics
are used for packaging material because they do not decay
when exposed to sunlight, water, or microorganisms. The
downside of this resistance to decay is that plastics can
remain unchanged in dumps and landfills for decades.
Alan Detrick/ Photo Researchers
C
Plastics are usually sorted by type before they are melted and
reprocessed. The plastics industry has a code to identify
common types of plastics. The numeral 1 is assigned to
polyethylene terephthalate (PET), which is used in softdrink bottles. The numeral 2 refers to high-density
polyethylene (HDPE), which is used in milk jugs and
shampoo bottles. These are the two types in greatest
demand. Carpets and clothing are made from
recycled PET fibers. Recycled HDPE is used as a
wood substitute for decks and benches. ■
Cigarette smoke contains
carbon monoxide. The
carbon monoxide from one
cigarette can remain in a
smoker’s blood for several
hours. Smoking increases the
risk of heart attacks because
the heart must pump harder
to deliver oxygen to cells
when the level of oxygen
is reduced. ■
Silicone Polymers
If you have worn hard contact
lenses or used shaving cream,
you have used a silicone.
Silicone polymers have chains
in which silicon and oxygen
alternate. The properties of
silicones depend on the groups
bonded to the silicon atoms
and the length of the chains.
CH3
CH3
O
CH3
CH3
O
Si
Si
CH3
CH3
Si
n
CH3
CH3
In silicone rubber and resins,
there are cross-links between
the chains. These silicones
repel water and remain elastic,
even at low temperatures.
They are used in space suits,
as gaskets in airplane windows, and as sealants that
are squeezed into place
and left to harden. ■
In polydimethylsiloxane, two
methyl groups are bonded to
each silicon atom in the
chain. Polydimethylsiloxane
is used as a lubricant in skin
and suntan lotions.
It is hard to detect colorless,
odorless carbon monoxide
gas. When it is inhaled, its
molecules bind to the
hemoglobin in red blood cells.
They bind about 200 times
more effectively than oxygen
molecules do. So less oxygen
reaches body tissues. Headaches, dizziness, nausea, and
drowsiness are symptoms of
low-level carbon monoxide
poisoning. Higher levels of
carbon monoxide are fatal.
The incomplete combustion
of fuel in gas furnaces and
space heaters produces carbon
monoxide. It also forms in
internal combustion engines
that are not well maintained.
In the United States, cars
have catalytic converters,
which convert carbon
monoxide to carbon dioxide.
Fleece clothing often contains postconsumer recycled (PCR) plastic.
Si
Carbon Monoxide
?
Did You Know...
Members of the Scott expedition to
the South Pole in 1912 may have died
because of tin. Their supply of paraffin
fuel leaked out through tiny holes in the
tin-soldered joints of the storage cans
because tin slowly changes to a powder
below 13°C.
Group 4A
R23